Maltitol crystals of particular forms, crystalline compositions containing them and processes for their preparation

ABSTRACT

The invention concerns modified maltitol crystals of particular forms, one pyramidal, the other prismatic. It further concerns crystalline compositions containing them and processes for their preparation.

[0001] The present invention concerns maltitol crystals of particularforms and crystalline compositions containing them. It also relates to aparticular process for obtaining these crystals and compositions.

[0002] For a very long time, maltitol was presentED only in the form oflow content syrups.

[0003] Then, maltitol was marketed in the form of amorphous and impurepowders.

[0004] To the knowledge of the Applicant company, it was only about 1980that prominence was given to maltitol crystals. Previously, this polyolwas not known as forming crystals easily.

[0005] The only crystalline form known up till now for maltitol is theanhydrous form, which is subject to wide-ranging patent protection onbehalf of the HAYASHIBARA company (U.S. Pat. No. 4,408,041).

[0006] The so-called “masse” techniques on the one hand and those ofwater crystallisation on the other, are today almost the only processesin industrial use. The products thus obtained are of very variablecrystallinity and are not all particularly well suited to certainapplications such as chewing-gum or chocolate.

[0007] On the other hand, there are other applications where theseproducts are not totally satisfactory. This is the case for example whenit is required to use maltitol to replace saccharose and lactose inpharmaceutical dry forms such as capsules, medicines of the solublepowder type, tablets and food preparations in powdered form to bedissolved. This is also the case when it is required to effect the samekind of substitution in sweetened foods such as powdered drinks,desserts, cake preparations or chocolate-flavoured or vanilla-flavouredbreakfast powders.

[0008] It is noted for these particular applications, particularly forpseudo-crystalline maltitol powders obtained by the “masse” techniqueand to a lesser degree for crystalline maltitol powders obtained bycrystallisation in water, that these have one or more defects inparticular for example those of not flowing of being liable to cake orto knot together, of dissolving only very slowly in water, of being badvehicles for compression or of not meeting the criteria foridentification and purity set by different pharmacopoeias.

[0009] In its wish to improve on the prior art, the Applicant companyhas sought to perfect maltitol compositions which do not have the flow,caking, dissolving or compression defects presented by known maltitolpowders. Admittedly, it might have been thought possible to meet theidentified need with other polyols. But, this is demonstrably not sosince none of them has characteristics of solubility, hygroscopicity,sweetened flavour and fusion as close to saccharose as maltitol.

[0010] And it is while working to perfect these compositions that theApplicant company was able to isolate, in a surprising and unexpectedway, two particular forms of maltitol crystals, one bipyramidal and theother prismatic.

[0011] It is to the credit of the Applicant company that it hassucceeded, after conducting extensive research, in explaining theexistence of these two forms of maltitol crystals. It has indeeddemonstrated that, against all expectation, the form of the maltitolcrystals was a function of the maltotriitol content of a maltitol syrupintended for crystallisation. The Applicant company has noted that bycontrolling the maltotriitol content of a maltitol syrup, it waspossible to direct the form of the maltitol crystals towards one orother of the forms or towards a mix of the two forms, when this maltitolsyrup is subjected to a crystallisation stage.

[0012] As a result, according to a first aspect, the invention relatesto modified maltitol crystals, characterised in that they arebipyramidal in form including two regular tetrahedrons juxtaposed bytheir square section base with sides of about 50 to 500 μm thusconstituting regular octahedrons with edge length of about 50 to 500 μm.

[0013] According to a second aspect, the invention also concernsmodified maltitol crystals, characterised in that they are prismatic inform ending with plane faces constituting a tetrahedron, and in thatthey are 100 to 400 μm long and about 20 to 100 μm wide.

[0014] The forms of crystallisation (bipyramidal or prismatic)inevitably have significant repercussions both for manufacture and forapplications. Thus, a semi-crystallised maltitol mass, including acertain percentage of prismatic crystals is more viscous than a massincluding the same percentage of bipyramidal crystals, all things beingequal in other respects, and this particularly when the crystals are ofsignificant size.

[0015] Therefore to prepare atomised maltitol, it is preferable toaccept suspensions which are very low in maltotriitol and additionallyincluding bipyramidal rather than prismatic crystals so as to avoidcaking. In other respects, the use of bipyramidal maltitol crystalsproves advantageous in the production of chocolate (more thickened massbefore refining), of chewing-gums (possibility of retaining a flexibletexture with a large amount of powdered maltitol), of pharmaceutical dryforms (greater consistency of flow) etc.

[0016] On the other hand, a prismatic form is more compressible andenables low crystal content caking, as is sometimes required(chewing-gums, chewing-gum centres to be sugar coated).

[0017] Other features and advantages of the invention will become fullyapparent on reading the following description, made by reference to theappended drawings, in which

[0018]FIGS. 1 and 2 show photographs by scanning electron microscope ofcrystals of bipyramidal form in compliance with the invention;

[0019]FIG. 3 shows a less enlarged photograph by scanning electronmicroscope of crystals identical to those in FIGS. 1 and 2;

[0020]FIG. 4 shows a photograph by scanning electron microscope of acrystal of prismatic form in compliance with the invention.

[0021] The invention therefore concerns first of all the bipyramidal andprismatic crystals illustrated in FIGS. 1 to 4.

[0022] The observations were carried out with the help of a JEOL 5410scanning electron microscope, after gold-plating the crystals with aJEOL JFC 1100 E metal sprayer (coating thickness 100 Angstroms).

[0023] The crystals were observed under a voltage of 2 and 5 kV. Thephotographs were taken on the microscope with an enlargement of 350times (FIG. 1), 500 times (FIG. 2), 50 times (FIG. 3) and 200 times(FIG. 4), then blown up during printing. However, there is a scaleinscribed on the photograph to show the actual size of the crystals.

[0024] The crystals in FIGS. 1 and 2 are of massive, bipyramidal form.More exactly, they have the form of two regular tetrahedrons, juxtaposedby their square section base, with sides from 50 to 500 μmapproximately, thus constituting regular octahedrons with edge length of50 to 500 μm approximately.

[0025]FIG. 3 shows that crystals in compliance with the invention arenot caked together or arranged in small aggregated clusters but are onthe contrary fully dissociated and individualised in relation to eachother.

[0026] The crystal in FIG. 4 looks like a rod with a pointed end. Moreexactly, it is prismatic in form and longer than it is wide(approximately 5 times longer than it is wide), ending in plane facesconstituting a tetrahedron. This rod is approximately 100 to 400 μm longby 20 to 100 μm wide.

[0027] The invention further concerns a crystalline maltitolcomposition, characterised in that it is constituted:

[0028] either by bipyramidal crystals complying with the invention;

[0029] or by prismatic crystals complying with the invention;

[0030] or by both bipyramidal and prismatic crystals.

[0031] The first essential characteristic of maltitol compositions inaccordance with the invention lies in the fact they are crystallised,which gives them very high stability in relation to humidity. As aresult they have only a slight tendency to cake or to knot together. Sothey are easy to use and it is not imperative to take draconianprecautions to guard against this danger.

[0032] These crystalline maltitol compositions all have a maltitolcontent greater than or equal to 87%, preferably greater than or equalto 92%, and more preferentially greater than or equal to 96%, andadvantageously have a reduced content of maltosyl-1,6 maltitol.

[0033] What essentially differentiates them from each other is themaltotriitol content.

[0034] Thus, when the crystalline maltitol composition is constituted bymaltitol crystals of bipyramidal form, it has a maltotriitol content, byweight of dry matter, of less than 1%.

[0035] When the crystalline maltitol composition is constituted bymaltitol crystals of prismatic form, it has a maltotriitol content, byweight of dry matter, greater than or equal to 4%.

[0036] And when the crystalline maltitol composition is constituted bymaltitol crystals of both bipyramidal and prismatic form, it has amaltotriitol content, by weight of dry matter, of between 1 and 4%.

[0037] The concept of content must be understood, in the case of thepresent invention, as corresponding to the percentage of maltitolexpressed as dry/dry weight in relation to the total carbohydratespresent in the crystalline maltitol composition. The carbohydrates maybe polyols such as in particular sorbitol, maltotriitol andmaltotetraitol.

[0038] The crystalline maltitol compositions complying with theinvention may contain, without their presence significantly altering thecrystallinity of these compositions, certain substances such as forexample strong sweeteners, colouring agents, pigments, scents,flavourings, vitamins, minerals, trace elements, active pharmaceuticalor veterinary ingredients, esters of fatty acids, organic or inorganicacids and their salts, proteinic matter such as proteins, amino acidsand enzymes.

[0039] The crystalline maltitol compositions are likely to be obtainedby crystallisation of a maltitol syrup with maltitol content greaterthan or equal to 87%, preferably greater than or equal to 92%, and morepreferentially greater than or equal to 96%, and a maltotriitol contentwhich, according to the composition which it is wished to obtain, isless than 1%, between 1 and 4%, or more than 4% by weight of dry matter.

[0040] One of the essential characteristics of the invention istherefore to vary the maltotriitol contents of the maltitol syrups to becrystallised while advantageously retaining a reduced content ofmaltosyl-1,6 maltitol.

[0041] It is for this reason that the invention further concerns aprocess to direct the form of the maltitol crystals, characterised inthat it consists in controlling the maltotriitol content of the maltitolsyrup to be crystallised. This control of the maltotriitol content ofthe maltitol syrup to be crystallised may be carried out upstream and/ordownstream of the crystallisation stage.

[0042] Upstream of the crystallisation stage:

[0043] during manufacture of the maltose syrup by using enzymes whichhydrolyse the maltotriose, and/or

[0044] by carrying out a molecular sieving of the maltose syrup intendedfor hydrogenation then crystallisation, and/or:

[0045] by carrying out a molecular sieving of the maltitol syrupintended for crystallisation and/or:

[0046] by carrying out an enzymatic hydrolysis of the maltitol syrupintended for crystallisation.

[0047] Downstream of the crystallisation stage:

[0048] by redissolving the crystalline maltitol composition in water andby carrying out a molecular sieving on the syrup thus obtained and/or anenzymatic hydrolysis and/or

[0049] by redissolving the crystalline maltitol composition in water andadding to it the amounts of maltotriitol required to obtain, afterrecrystallisation, a new crystalline maltitol composition complying withthe invention with the required maltotriitol content.

[0050] All these possibilities for controlling the maltotriitol contentmay be used singly or in combination with each other.

[0051] From what precedes, it therefore follows that the process fordirecting the form of the maltitol crystals, in compliance with theinvention, offers great flexibility in use. Indeed it enables switchingequally well from bipyramidal form crystals to prismatic form crystalsand vice versa.

[0052] To prepare the maltitol syrup which enables, aftercrystallisation, the compositions complying with the invention to beobtained, the process described below or an equivalent process is used.

[0053] The first step in the process is known per se. It consists inliquefying a starch slurry which may be of any botanical origin: it mayderive from corn, maize or potato for example.

[0054] This starch or flour slurry has acid added in the case of aso-called acid liquefaction, or an α-amylase added in the case ofenzymatic liquefaction.

[0055] In the process complying with the invention, it is preferred tocarry out a controlled hydrolysis of the starch slurry so as to obtain aliquefied starch slurry with a low transformation rate. In this way,conditions of temperature, of pH, of enzyme and calcium content, knownto the professional, are determined in such a way that they enable aDE(Dextrose Equivalent) to be obtained of less than 10, preferably lessthan 6, and more particularly less than 4.

[0056] Preferably, the liquefaction stage is conducted in twosub-stages, the first consisting in heating the starch slurry, for a fewminutes and at a temperature of between 105 and 108° C., in the presenceof an α-amylase (TERMAMYL® 120L type marketed by the NOVO company) and acalcium based activator, the second consisting in heating the starchslurry thus treated to a temperature of between 95 and 100° C. for oneto two hours.

[0057] Once the liquefaction stage is complete, in the conditions of drymatter content, of pH, of enzyme and calcium content that are well knownto the professional, the next step is the inhibition of the α-amylase.This inhibition of the α-amylase may preferably be carried out thermallyby initiating at the end of the liquefaction process a thermal shocklasting a few seconds at a temperature exceeding or equal to 130° C.

[0058] Following this the saccharification stage is carried out. Duringthis stage, the liquefied starch slurry is first subjected to the actionof a maltogenic α-amylase, such as that marketed by the NOVO company,under the name Maltogénase®. During this first saccharification stage,the maltogenic α-amylase can be added in a single dose or in severaldoses.

[0059] At this stage of the process, it is already possible to controlthe maltotriose content (which after hydrogenation leads tomaltotriitol) formed during the hydrolysis of the starch, by adjustingthe amount of maltogenic α-amylase as a function of the maltotriosecontent and therefore of the form of the maltitol crystals that it iswished to obtain.

[0060] The next step, after allowing the maltogenic α-amylase to react,is the saccharification of the liquefied starch slurry by means of aβ-amylase such as that marketed by the GENENCOR company under the nameSPEZYME® BBA 1500.

[0061] During these stages, it is appropriate to combine with themaltogenic action enzymes (maltogenic α-amylase and β-amylase) an enzymewhich specifically hydrolyses the α-1,6 starch bonds. This addition of adisconnecting enzyme enables on the one hand hydrolysis reactions to beaccelerated without simultaneously accelerating reversion reactions and,on the other hand, the amount of strongly connected oligosaccharidesnormally resistant to the action of maltogenic enzymes to be reduced.

[0062] This disconnecting enzyme can be added at the same time as themaltogenic α-amylase is added or at the same time as the β-amylase isadded.

[0063] This disconnecting enzyme is selected from the group constitutedby the pullulanases and the isoamylases.

[0064] The pullulanase is for example that marketed by the ABM companyunder the name PULLUZYMER®.

[0065] The isoamylase is for example that marketed by the HAYASHIBAPAcompany.

[0066] The process is implemented to advantage in the presence ofisoamylase for which the Applicant company has noted that it not onlyenabled a maltose syrup with a higher maltose content to be obtainedthan by using a pullulanase, but it also enabled a maltose syrup with areduced content of maltosyl-1,6 maltose and therefore of maltosyl-1,6maltitol after hydrogenation to be obtained.

[0067] The saccharification stage can also be conducted totally orpartially in the presence of fungal α-amylase.

[0068] At the end of saccharification, it is possible to add a littleα-amylase, which generally improves the subsequent filtration stages.The amounts and conditions of action of the different enzymes used inthe liquefaction and saccharification stages of the starch slurry aregenerally those which are recommended for the hydrolysis of starch andare well known to the person skilled in the art.

[0069] Saccharification is carried out until the maltose hydrolysatecontains at least 87%, preferably at least 92%, and more preferentiallyat least 96% by weight of maltose.

[0070] The hydrolysate thus saccharified is then filtered through apre-coated filter or by micro-filtration through membranes, thende-mineralised.

[0071] At this stage in the process, it may be possible to carry out onthe saccharified and purified hydrolysate, a stage of maltosecrystallisation or molecular sieving, this molecular sieving stageenabling the maltotriose content of the maltose syrup to be controlled,i. e. to more or less deplete, or not at all, the maltose syrup ofmaltotriose. This molecular sieving stage may thus also enable therecovery of:

[0072] either a first fraction enriched in maltose and higheroligosaccharides and a second fraction enriched in glucose;

[0073] or a first fraction enriched in higher oligosaccharides and asecond fraction enriched in maltose and glucose;

[0074] or, lastly, a first fraction enriched in higher oligosaccharides,a second fraction enriched in maltose and a third fraction enriched inglucose.

[0075] This molecular sieving stage may consist, for example, of achromatographic separation stage or a separation by membrane stage.

[0076] The chromatographic fractionation stage is conducted in a wayknown per se, discontinuously or continuously (simulated fluid bed), onadsorbents of the cationic resin type, or on highly acid zeolites,preferentially charged with the help of alkaline or alkaline-earth ionssuch as calcium or magnesium but more preferentially with the help ofsodium ions.

[0077] Instead and in place of the chromatographic separation stage, itis possible to implement a separation stage by nano-filtration bymembranes. Membranes of various pore diameters are manufactured from anumber of polymers and copolymers of the polysulphone, polyamide,polyacrylonitrate, polycarbonate, polyphurane types, etc.

[0078] Examples of the use of such membranes are described particularlyin the documents U.S. Pat. No. 4,511,654, U.S. Pat. No. 4,429,122 andWO-A-95/10627.

[0079] The maltose hydrolysate thus obtained may then be easilyhydrogenated catalytically.

[0080] The hydrogenation of such a hydrolysate is carried out incompliance with the rules of the art which lead for example to theproduction of sorbitol from glucose.

[0081] For this stage ruthenium based catalysts can be used as well asRANEY nickel catalysts. The use of RANEY nickel catalysts is howeverpreferred since they are less expensive.

[0082] In practice, from 1 to 10% by weight of catalyst compared withthe dry matter of the hydrolysate subjected to hydrogenation is used.Hydrogenation is carried out preferably on a hydrolysate the dry matterof which is between 15 and 50%, in practice in the area of 30 to 45%, atbetween 20 and 200 bars of hydrogen pressure. It can be carried outcontinuously or discontinuously.

[0083] When the operation is discontinuous, the hydrogen pressure usedis generally between 30 and 60 bars and the temperature at whichhydrogenation occurs is between 100 and 150° C. Care is also taken tomaintain the pH of the hydrogenation medium by the addition of sodiumhydroxide or sodium carbonate for example, but without exceeding a pH of9.0. This way of proceeding enables the appearance of cracking orisomerisation products to be avoided.

[0084] The reaction is stopped when the reducing sugars content of thereaction medium has dropped below 1%, preferably even below 0.5% andmore particularly below 0.1%.

[0085] After the reaction medium has cooled, the catalyst is eliminatedby filtration and the maltitol syrup thus obtained is demineralised oncationic and anionic resins. At this stage, the syrups contain at least85% maltitol.

[0086] According to a first version of the process, a series of steps isapplied to the maltitol syrup obtained in the preceding hydrogenationstage as follows:

[0087] possibly carrying out a chromatographic fractionation, known perse, so as to obtain a maltitol rich fraction and a more or less richmaltotriitol fraction as a function of the form of crystals required;

[0088] concentrating the maltitol rich fraction;

[0089] crystallising and separating the formed maltitol crystals;

[0090] recycling the crystallisation mother-liquors upstream of thechromatographic fractionation stage.

[0091] According to a second version of the process, a series of stepsis applied to the maltitol syrup obtained in the preceding hydrogenationstage as follows:

[0092] concentrating the maltitol syrup;

[0093] crystallising and separating the formed maltitol crystals.

[0094] According to a third version of the process, a series of steps isapplied to the maltitol syrup obtained in the preceding hydrogenationstage as follows:

[0095] possibly carrying out an enzymatic hydrolysis of the maltitolsyrup, by means for example of an amyloglucosidase whether immobilisedor not so as to convert any possibly present maltotriitol into maltitol;

[0096] concentrating the maltitol syrup thus obtained;

[0097] crystallising and separating the formed maltitol crystals.

[0098] According to another version of the process complying with theinvention, a series of steps is applied to the maltose hydrolysateobtained after saccharification as follows:

[0099] possibly carrying out a chromatographic fractionation, known perse, so as to obtain a maltose rich and more or less maltotriose richfraction;

[0100] hydrogenating the maltose rich fraction;

[0101] crystallising and separating the formed maltitol crystals.

[0102] The invention will now be described with the help of thefollowing example provided solely by way of illustration andnon-restrictively.

EXAMPLE

[0103] 1. Test Conditions

[0104] The syrup to be crystallised is concentrated to 80% dry matter,placed in a laboratory crystallising dish and stabilised at atemperature of 50° C., then an initial nucleus of MALTISORB®(crystallised maltitol marketed by the Applicant company) at the rate of1%/dry matter, is 10 added and the crystallising dish is cooled underslow stirring to 20° C., at the rate of 0.3° C. per hour. After spinningand clearing with ethanol, the crystals are dried and observed under ascanning electron microscope.

[0105] 2. Results

[0106] Different bases are used; their composition and the form of thecrystals obtained are summarised in the following table. COMPOSITIONCRYSTAL APPEARANCE DP2H > 99% homogeneous, bipyramidal in form DP2H:93.5% heterogeneous, bipyramidal DP3H: 3.8% and prismatic in form Sup.:2.7% DP1H: 5.2% DP2H: 90.1% homogeneous, DP3H: 0.9% bipyramidal in formDP4H: 3.8% DP2H: 96% homogeneous, DP3H: 4% prismatic in form

1. Modified maltitol crystals, characterised in that they arebipyramidal in form including two regular tetrahedrons juxtaposed bytheir square section base with sides of 50 to 500 μm approximately, thusconstituting regular octahedrons with edge length of approximately 50 to500 μm.
 2. A crystalline maltitol composition, characterised in that itincludes essentially maltitol crystals according to claim 1 and that ithas a maltitol content greater than or equal to 87%, preferably greaterthan or equal to 92%, and more preferentially greater than or equal to96% and a maltotriitol content by weight of dry matter, lower than 1%.3. A manufacturing process of a composition in accordance with claim 2 ,characterised in that it consists in crystallising a maltitol syruphaving a maltitol content greater than or equal to 87%, preferablygreater than or equal to 92%, and more preferentially greater than orequal to 96% and a maltotriitol content lower than 1% by weight of drymatter.
 4. Modified maltitol crystals, characterised in that they areprismatic in form, ending in plane faces constituting a tetrahedron, andthat they are 100 to 400 μm long and about 20 to 100 μm wide.
 5. Acrystalline maltitol composition, characterised in that it includesessentially maltitol crystals according to claim 4 and that it has amaltitol content greater than or equal to 87%, preferably greater thanor equal to 92%, and more preferentially greater than or equal to 96%and a maltotriitol content greater than or equal to 4%.
 6. Amanufacturing process of a composition in accordance with claim 5 ,characterised in that it consists in crystallising a maltitol syruphaving a maltitol content greater than or equal to 87%, preferablygreater than or equal to 92%, and more preferentially greater than orequal to 96% and a maltotriitol content greater than or equal to 4% byweight of dry matter.
 7. A crystalline maltitol composition,characterised in that it includes maltitol crystals according to claims1 and 4 and that it has a maltitol content greater than or equal to 87%,preferably greater than or equal to 92%, and more preferentially greaterthan or equal to 96% and a maltotriitol content, by weight of drymatter, of between 1 and 4%.
 8. A manufacturing process of a compositionin accordance with claim 7 , characterised in that it consists incrystallising a maltitol syrup having a maltitol content greater than orequal to 87%, preferably greater than or equal to 92%, and morepreferentially greater than or equal to 96% and a maltotriitol content,by weight of dry matter, of between 1 and 4%.
 9. A process for directingthe form of the maltitol crystals, characterised in that it consists incontrolling the maltotriitol content of the maltitol syrup to becrystallised.
 10. The use of maltotriitol to modify or control the formof maltitol crystals.